This invention relates to apparatus used in separating a portion of fluid for use as a sample from a flowing stream of fluid. Examples of such apparatus may be found in U.S. Pat. Nos. 3,921,458 (Logan), 3,595,087 (Starks), and 3,803,921 (Dieterich). It can be readily seen that particulate matter in the sampled stream is not excluded from entering the sample probes of these patents. This invention further relates to obtaining a fluid sample which is substantially reduced in particulate content.
The presence of particulate matter entrained in a flowing fluid adds to the difficulty of obtaining a sample of the fluid. Often, particulate matter should not be present in a sample. For example, when a sample stream is allowed to flow to a chromatographic analyzer, particles must be removed from the stream to prevent malfunction of the analyzer. Particle removal from a sample stream can be accomplished by means of apparatus familiar to those skilled in the art such as filters or cyclones. However, such particle removal apparatus must be designed, purchased, installed, and maintained, sometimes at significant cost. Tubing and equipment used to contain and process a sample can become plugged with particles, causing interruption of sample flow. The removed particles must be disposed of in some manner. Thus, it is often desirable to exclude particulate matter at the point of taking a sample, that is, to obtain a sample of fluid only, leaving all particles in the sampled stream. In some cases, a sample may be removed from a flowing stream through filter material immersed in the stream, so that particles collected on the filter material are swept away by the fluid stream. But this may not be feasible due to unavailability of filter material compatible with the stream to be sampled, rapid blinding of the filter material by particulate matter, or other problems.
Though it may not be possible to exclude all particulate matter at the point of sampling, it is desirable to exclude as much as possible, thus reducing the magnitude of the problems associated with the presence of particulate matter. For example, consider a case where a sample system filter rapidly blinds, or clogs, and hinders fluid flow through it, so that it is necessary to change or clean the filter daily. By excluding particles at the point of sampling, the amount of particulate matter collected by the filter might be reduced to a more tolerable level. Changing a disposable filter element or cleaning a reusable element once a week might be acceptable, where changing or cleaning once a day would not.